The internet outage affected high-traffic sites including The New York Times, Reddit and Amazon.com. TheStreet.com also was affected.
"This outage was broad and severe, and we’re truly sorry for the impact to our customers and everyone who relies on them," Fastly Senior Vice President Nick Rockwell said in a statement.
Fastly shares at last check dropped 2.3% to $54.90.
The company on May 12 began a software deployment. The deployment introduced a bug that could be triggered by a specific customer configuration under specific circumstances.
On June 8, one of its customers pushed all the right buttons to prompt the bug that took down internet websites worldwide.
The company said it was deploying a bug fix across its network as "quickly and safely as possible." Fastly also says it is conducting a complete review of the processes and practices it followed during the outage.
"Even though there were specific conditions that triggered this outage, we should have anticipated it," the company said. "We apologize to our customers and those who rely on them for the outage and sincerely thank the community for its support."
In May, Fastly shares plunged after the company lowered its second-quarter and full-year revenue forecasts and said that its chief financial officer was stepping down.
Piper Sandler analysts James Fish and Quinton Gabrielli wrote in a research note that Fastly’s lead metrics and organic growth deceleration, landscape, and valuation “leave us incrementally more concerned.” The affirmed a neutral rating on the shares.